Metastasis is the major cause of mortality for cancer patients. However, the genetic basis for tumor progression and metastasis is largely unknown. Given that multiple genetic alterations occur during tumor initiation and progression, it has been difficult to find families with inherited mutations for both tumorigenesis and metastasis. The genomes of malignant tumor cells are often destabilized, which makes it a daunting challenge to pinpoint the causative alterations for tumor progression. Furthermore, metastasis involves multiple tissues and it is particularly difficult to study the process in tissue culture cells. Finally, tumor progression in humans and mammals takes a long period of time, which adds additional complication for experimental research. We have developed a Drosophila model for metastasis and have performed a genome-wide screen to identify mutations promoting tumor progression and metastasis. About 100 mutations have been identified which collaborate with oncogenic Ras in promoting tumor progression and metastasis in flies. These fly tumors exhibit a full spectrum of metastatic phenotypes observed in human malignant cancers including loss of cell adhesion, degradation of basement membrane, migration, invasion, and secondary tumor formation. This fly tumor metastasis model and the identified mutations provide a unique opportunity to dissect metastatic behavior in vivo and the mechanism underlying such phenomenon. We propose the following specific aims: (1) Genetic and phenotypic characterization for the recovered metastasis-promoting mutations to identify the genes that disrupted by these alterations and to document the phenotypic consequence caused by these mutations;and (2) Study molecular mechanism underlying oncogenic cooperation that promotes tumor progression and metastasis. We hope that these studies will improve our understanding of the genetic basis for metastatic behavior. Given that many molecules and pathways are conserved from flies to humans, it is further hoped that these experiments will also contribute to our understanding of some aspects of tumor progression and metastasis in humans.